Extended life fluorescence polyvinyl chloride sheeting

ABSTRACT

An extended life fluorescent polyvinyl chloride sheeting and a method for forming the sheeting are disclosed. The sheeting includes a polyvinyl chloride film having a fluorescent colorant incorporated therein. A protective polymer layer is attached to the polyvinyl chloride film. A light filtering agent is incorporated into the protective layer, wherein the filter agent blocks the 425 nm and lower wavelengths of the visible spectrum.

RELATED APPLICATION

[0001] This present application claims the benefit of U.S. ProvisionalPatent Application No. 60/072,026, filed on Jan. 21, 1998. Thisapplication is a continuation of application Ser. No. 09/233,965, filedon Jan. 20, 1999. The entire teachings of each application areincorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The advantages of the high visibility of fluorescent materials iswell known. However, poor color fastness in the presence of sunlight hasmade their use in some applications limited to short-lived, temporaryapplications. These applications include roadside work zone signs,vehicle conspicuity signs, etc.

[0003] Plasticized polyvinyl chloride has been used extensively forretroreflective sheeting applications. In roadside work zoneapplications, flexible, roll-up signage formed of polyvinyl chlorideprovides an improved safety upon impact by a vehicle over rigid signage.However, the fluorescent colored polyvinyl chloride signs can fade to aclear film quickly after exposure to sunlight as the fluorescentcolorant is consumed with lengthy exposure to ultraviolet light emittedby the sun. However, the retroreflective prism structure continues tofunction.

[0004] Some polymers, such as polycarbonate, that have a fluorescentcolorant include a hindered amine light stabilizer compound.

SUMMARY OF THE INVENTION

[0005] The present invention includes an extended life fluorescentpolyvinyl chloride sheeting and a method for forming the sheeting.

[0006] The sheeting includes a polyvinyl chloride film having afluorescent colorant incorporated therein. A protective polymer layer isattached to the polyvinyl chloride film. A light filtering agent isincorporated into the protective polymer layer, wherein the filter agentblocks the 425 nm and lower wavelengths of the visible spectrum.

[0007] The method includes providing a polyvinyl chloride film having afluorescent colorant incorporated therein. A protective polymer layer isattached to the polyvinyl chloride film. The protective polymer layerincludes a light filtering agent that blocks the 425 nm and lowerwavelengths of the visible spectrum, thereby forming the extended lifefluorescent polyvinyl chloride sheeting.

[0008] The present invention has an advantage of providing fluorescentprotection to a polyvinyl chloride sheeting while providing solventresistance, printability, low coefficient of friction and canincorporate water shedding properties, such as hydrophobic andhydrophilic additives where desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a chart of the results of an accelerated weatheringcolor test of a first sample of the present invention and a firststandard product.

[0010]FIG. 2 is a chart of the results of an accelerated weatheringcolor test of a second sample of the present invention and a secondstandard product.

[0011]FIG. 3 is a chart of the results of an accelerated weatheringcolor test of the second sample of the present invention and second andthird standard products.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention. All percentagesand parts are by weight unless otherwise indicated.

[0013] Retroreflective materials are typically formed of a sheet ofthermoplastic, which has a colorant mixed therein with the polymers.Attached to the sheet of thermoplastic is an array of cube-corner orprismatic retroreflectors as described in U.S. Pat. No. 3,712,706,issued to Stamm on Jan. 23, 1973, the teachings of which areincorporated herein in their entirety by reference. Generally, theprisms are made by forming a master die on a flat surface of a metalplate or other suitable material. To form the cube-corner, three seriesof parallel equidistant intersecting V-shaped grooves 60 degrees apartare inscribed in the plate. The die is then used to process the desiredcube-corner array into a flat plastic surface. When the groove angle is70 degrees, 31 minutes, 43.6 seconds, the angle formed by theintersection of two cube faces (dihedral angle) is 90 degrees and theincident light is retroreflected back to the source.

[0014] The efficiency of a retroreflective structure is the measure ofthe amount of incident light returned within a cone diverging from theaxis of retroreflection. A distortion of the prismatic structureadversely affects the efficiency. Furthermore, cube-cornerretroreflective elements have low angularity at some orientation angles,for instance, the elements will only brightly reflect light thatimpinges on it within a narrow angular range centering approximately onits optical axis. Low angularity arises from the inherent nature ofthese elements which are trihedral structures having three mutuallyperpendicular lateral faces. The elements are arranged so that the lightto be retroreflected impinges into the internal space defined by thefaces, and the retroreflection of the impinging light occurs by internalretroreflection of the light from face to face of the element. Impinginglight that is inclined substantially away from the optical axis of theelement (which is a trisection of the internal space defined by thefaces of the element) strikes the face at an angle less than itscritical angle, thereby passing through the face rather than beingreflected. Further details concerning the structures and the operationof cube-corner microprisms can be found in U.S. Pat. No. 3,684,348,issued to Rowland on Aug. 15, 1972, the teachings of which areincorporated by reference herein in their entirety. The disclosed methodis for forming cube-corner microprisms in a cooperatively configuredmold. The prisms are bonded to sheeting which is applied thereover toprovide a composite structure in which cube-corner microprisms projectfrom one surface of the sheeting.

[0015] The array of retroreflectors includes optical elements that areknown in the art, such as cube-corner prisms, four-sided prisms, Fresnellenses, rounded lenses, etc. In one embodiment, the array ofretroreflectors has a window side and a facet side. The array ofretroreflectors are formed of a transparent flexible polymer polyvinylchloride. Preferably, the polymer is cast in a mold with a monomer oroligomer, and the polymerization is initiated by ultraviolet radiation.Preferably, the array of retroreflectors is formed of cube-corner prismelements having a length along each cube side edge in the range ofbetween about 0.003 and 0.02 inches (0.076 and 0.51 mm). In a preferredembodiment, the prism elements have a length along each cube-side edgein the range of between 0.0049 and 0.02 inches (0.124 and 0.51 mm). In aparticularly preferred embodiment, each cube-side edge has a length ofabout 0.0049 inches (0.124 mm).

[0016] An adhesive can be applied to the prism facets for attaching abacking layer to the retroreflective structure. If an adhesive isemployed on the prism facets, the adhesive can cause the surface of theprisms to wet, thereby destroying the air interface and eliminating theability of the prism to retroreflect. As a result, the reflectivecoating is preferably deposited on the surface of the dihedral facets.Typically, the reflective coating is formed by sputtering aluminum,silver or gold or by vacuum metalization. Alternatively, metal lacquers,dielectric coatings and other specular coating materials can beemployed.

[0017] The retroreflective structure 24 can be formed by numerousmethods. Some of the methods for forming a retroreflective structure aredisclosed in U.S. Pat. No. 3,684,348, issued to Rowland on Aug. 15,1972; U.S. Pat. No. 3,689,346, issued to Rowland on Sep. 5, 1972; U.S.Pat. No. 3,811,983, issued to Rowland on May 21, 1974; U.S. Pat. No.3,830,682, issued to Rowland on Aug. 20, 1974; U.S. Pat. No. 3,975,083,issued to Rowland on Aug. 17, 1976; U.S. Pat. No. 4,332,847, issued toRowland on Jun. 1, 1982; U.S. Pat. No. 4,801,193, issued to Martin onJan. 31, 1989; U.S. Pat. No. 5,229,882, issued to Rowland on Jul. 20,1993; U.S. Pat. No. 5,236,751, issued to Martin et al. on Aug. 17, 1993;U.S. Pat. No. 5,264,063, issued to Martin on Nov. 23, 1992; U.S. Pat.No. 5,376,431, issued to Rowland on Dec. 27, 1994; U.S. Pat. No.5,491,586, issued to Phillips on Feb. 13, 1996; U.S. Pat. No. 5,512,219,issued to Rowland on Apr. 30, 1996; U.S. Pat. No. 5,558,740, issued toBernard et al. on Sep. 24, 1996; U.S. Pat. No. 5,592,330, issued toBernard on Jan. 7, 1997; and U.S. Pat. No. 5,637,173, issued to Martinet al. on Jun. 10, 1997. The teachings of each patent are incorporatedherein by reference.

[0018] The advantages of the high visibility of fluorescent materials iswell known, but their poor color fastness in the presence of ultravioletlight has made their use in some important applications, such asroadside work zone, vehicle conspicuity, etc., limited to short-lived,temporary applications.

[0019] Plasticized vinyl has been used extensively for retroreflectivesheeting applications. In applications, such as roadside work zones, ithas also been well established that flexible so-called “roll-up” signageusually made of highly plasticized polyvinyl chloride provide greatlyimproved safety upon impact over rigid signage.

[0020] The use of a free radical absorber of the hindered amine lightstabilizer type, such as 2,2,6,6-tetramethyl piperdine, has been used toimprove the color fastness of polycarbonate colored with thethioxanthene, perylene imide, and thioindigold fluorescent colorants(U.S. Pat. No. 5,605,761).

[0021] It has been found that by use of a protective polymer layer orcoating or film layer made of polyacrylate, polyurethane, orpolyurethane acrylates which incorporate ultraviolet absorbers of thebenzophenone or benzotriazole-type along with a light filtering agentwhich blocks out the short wavelengths of the visible spectrum (425 nmand lower) over a highly plasticized flexible fluorescent polyvinylchloride sheeting containing a suitable hindered amine, color fastnesscan be greatly improved. The wavelengths of visible light extend betweenabout 400 nm for the extreme violet and about 720 nm for the deep red.The visible light filtering agent should impart color that can obscurethe desirable daytime visibility of the fluorescent product. A suitablevisible light filtering agent is Color Index Solvent Yellow 93. Asuitable amount of filtering agent is in a range of between about 0.05and 5.0 percent. A preferred range is between about 0.1 and 1.5 percent.A suitable hindered amine for use with polyvinyl chloride isbis-(1,2,2,6,6-tetramethyl-4-piperidinyl) sebacate. A suitable amount ofhindered amine is in a range of between about 0.1 and 7.0 percent. Apreferred range is between about 0.2 and 1.5 percent.

[0022] Through selection of coating ingredients in the top coatprotective polymer layer, the fluorescent protection features can becoupled with a wide variety of different performance propertiesincluding but not limited to cold temperature flexibility, solventresistance, printability, low coefficient of friction, and specializedwater shedding properties (i.e. hydrophobic, hydrophilic).

[0023] The colors of principal interest in the area of fluorescentretroreflective sheeting are lime-yellow and red-orange.

[0024] The base material of wavelength filtering layer can be a polymerfilm, such as polyvinyl chloride, polyacrylate, polyurethane,polyvinylidene chloride, fluoropolymer, or highly stabilized copolymers,such as vinylidene fluoride-hexafluoropropylene. This film can belaminated directly to fluorescent colored layer through heat andpressure in some cases, such as some urethanes, or by use of an adhesivelayer. The thickness of the wavelength filtering layer can be in therange of between about 0.1 and 10 mils (0.00254 and 0.254 mm). The basematerial of the wavelength filtering layer can also be applied to thefluorescent colored layer as a coating. This coating can be solventborne, water-based, two-part, or radiation curable in nature.

[0025] The wavelength filtering layer is protective to the colorant inthe fluorescent colored layer by incorporation of ultraviolet lightabsorbers or selected colorants or both which can block the wavelengthsthat are destructive to the colorant but still allow the day brightcolor to be visible. The daytime visibility of the product can betemporarily enhanced by the incorporation of some fluorescent colorantinto the wavelength filtering layer, provided that the wavelengthsgenerated by fluorescent colorant in the filtering layer are notdestructive to the primary fluorescent colorant in the fluorescentcolored layer.

[0026] For the fluorescent colored layer, a base polymer of polyvinylchloride is preferred. Incorporated into this layer is the primaryfluorescent colorant of the product. The most commonly used, widelyavailable, and lowest cost fluorescent colorants are the xanthene basedfluorescent dyes. This group, which encompasses both the fluorenes andthe fluorones, includes such dyes as fluoresceins, rhodamines, eosines,phloxines, uranines, succineins, sacchareins, rosamines, and rhodols.The dyes are noted for their brilliant daytime colors, high intensitycolor compatible fluorescence, and poor light fastness. Otherfluorescent dyes displaying better light fastness include pyranines,anthraquinones, benzopyrans, thioxanthenes and perylene imides.

[0027] The prism layer can be compression molded or cast directly ontothe fluorescent colored layer or attached by means of a tiecoat. Theprism layer can be formed of polyvinyl chloride, an acrylate or othersuitable polymer.

[0028] This prismatic sheeting configuration can be sealed to any numberof backing materials by radio frequency, thermal, or sonic weldingmethods. The daytime color saturation (chroma) properties of atransparent fluorescent material are increased if backed by a whitelayer, it is desirable to have the backing be white in color on thesurface behind the prisms. Alternatively, the prismatic material can bemetalized in an aesthetically appealing pattern and laminated to a whitepressure sensitive substrate adhesive. Similarly, a pattern can beprinted onto the film prior to casting, or onto the backs of the prismsafter casting, using a white ink to enhance the daytime chroma. However,these methods enhance the daytime fluorescent color at the expense ofsome of the retroreflective area, because the non-metalized prisms thathave their facets covered with adhesive do not maintain adifferentiation in refractive index that is sufficiently large forinternal reflection to occur.

[0029] Both of the latter construction alternatives have the advantageof not having an air gap in the construction behind the prism layer.Elimination of the air gap can help augment the physical durability ofthe sheeting, because each layer of the product has about 100% of itssurface bonded to its adjacent layers.

[0030] If a reflective material that is environmentally stable yetwhiter than aluminum can be coated onto the prism facets, it can allow afully metalized product to have an adequate “cap Y” to produce a desireddaytime color. Silver, chromium, gold, palladium, and platinum are alsopossibilities.

[0031] The product can conform to the Minnesota Department ofTransportation Specification 1710 for Fluorescent Orange RetroreflectiveSheeting for Use on Work Zone Traffic Control Devices, the teachings ofwhich are incorporated herein by reference in their entirety. It definesa color box (see Product Testing Requirements and Specificationsection), reflectance limits (30 minimum new, 20 minimum to 45 maximumfor weathered (500 Weatherometer hours)), and a table (B) of MinimumCoefficients of Retroreflection approximate the 1,300 hour colorretention in a xenon lamp accelerated weathering device.

[0032] A series of test samples was prepared for accelerated weatheringtesting under ASTM G26. The teachings of ASTM G26 are incorporatedherein by reference in their entirety.

EXAMPLE 1

[0033] A fluorescent lime (yellow-green) colored microprismatic productwas formed having a polyvinyl chloride base film. The polyvinyl chloridebase film was highly plasticized using phthalate monomeric plasticizersand a xanthene solvent yellow as a colorant with a benzophenoneultraviolet absorber additive having a thickness of about 250μ thick.The film was further protected with a 7μ thick topcoat based on aflexible urethane acrylate oligomer, and containing a benzotriazoleultraviolet absorber and a hindered amine light stabilizer, and C.I.Solvent Yellow 93. This configuration of polyvinyl chloride andadditives absorbed eighty-five percent or more of the light havingwavelengths of 450 nm and shorter.

EXAMPLE 2

[0034] A fluorescent orange colored microprismatic product was formedhaving a polyvinyl chloride base film. The 350μ thick polyvinyl chloridebase film was highly plasticized using phthalate monomeric plasticizersand colored with a fluorescent orange, thioxanthone colorant, abenzophenone ultraviolet absorber additive, and hindered amine lightstabilizer. The film was further protected with a clear, 100μ thick,polyvinyl chloride based top film containing a benzophenone ultravioletabsorber additive.

EXAMPLE 3

[0035] A fluorescent orange colored microprismatic standard Product Awas formed having a polyvinyl chloride base film. The 250μ thick,polyvinyl chloride base film was highly plasticized using phthalatemonomeric plasticizers and a mixture of a xanthene solvent yellow andrhodamine B as colorants.

EXAMPLE 4

[0036] A fluorescent orange colored microprismatic standard Product Bwas formed having a polyvinyl chloride base film. The polyvinyl chloridebase film is highly plasticized using phthalate monomeric plasticizers.The film was made from a lamination of two 150μ thick polyvinyl chloridefilms. The first polyvinyl chloride film included a non-fluorescent butvery light stable combination of a transparent diazo yellow and organicred pigments. The second polyvinyl chloride film included the highlyfluorescent but comparatively fugitive combination of colorants used inStandard Product A.

EXAMPLE 5

[0037] A fluorescent lime (yellow-green) colored microprismatic standardProduct C was formed having a polyvinyl chloride base film. The 250μthick, polyvinyl chloride base film was highly plasticized usingphthalate monomeric plasticizers and a xanthene solvent yellow colorant.

[0038] All of the aforementioned Examples 1-5 included the samemicroprismatic array composed of a cross-linked acrylated urethaneester. Each of the prismatic films was sealed by radio frequency weldingto a polymeric plasticized, opaque white, textured, polyvinyl chloridebacking material for purposes of this accelerated weather testing.

[0039] All of the samples were mounted onto an aluminum panel withpressure sensitive adhesive and tested in an Atlas model C35 XenonWeatherometer in accordance with the ASTM G26 test method for a total of1,500 hours. The teachings of ASTM G26 are incorporated herein in theirentirety. The samples were evaluated periodically throughout theduration of the test for color change using a HunterLab LabScan II,LS-6000 Spectrophotometer.

[0040] Minimal movement in color coordinates can show color stability.The orange colorant in a standard product can fade to yellow (out of thecolor box) after approximately 48 hours in a carbon-arc Weatherometerwhile the orange colorant in a sample of the present invention can stillbe in the color box after fifteen hundred hours of exposure. An exampleof a color box is shown in FIG. 2 as defined by the orange color regionboundary (Coordinate 1, x=0.550, y=0.360; Coordinate 2, x=0.630,y=0.370; Coordinate 3, x=0.581, y=0.418; Coordinate 4, x=0.516,y=0.394). The color box coordinates are disclosed in ASTM D4956-95,Table 10 for Color Specification Limits (Daytime) for white, yellow,orange, green, red, blue and brown. The teachings of ASTM D4965-95 areherein incorporated by reference in their entirety. Spectrophotometer orcolorimeter having 45°/0° or 0°/45° illumination and viewing geometry issuitable for measuring color. Color coordinates are defined bytristimulus coordinates corresponding to the CIE 1931 StandardColorimetric System by standard illuminant C.

[0041]FIG. 1 shows the degree of color change (distance moved) in CIE1931 standard color space for Standard Product C (described in Example5) after 375 hours of testing was greater than the sample described inExample 1 after 1,500 hours of exposure testing. The date point labelsindicate hours of exposure in the Weatherometer.

[0042]FIG. 2 shows the rapid color change of fluorescent orange StandardProduct A (as described in Example 3) after only 100 hours of exposurewhich resulted in a change in color from orange (0.595, 0.4) to yellow(0.498, 0.47) as compared to the color stability of a sample of thepresent invention, as described in Example 2, after 1,500 hours ofexposure, which maintained its orange color.

[0043]FIG. 3 shows the color fastness performance of two commerciallyavailable products compared to the present invention as described inExample 2. Standard Product B (Example 4) exhibited rapid color changeover the first 125 hours of exposure as the conventional fluorescentcolorants faded and then became fairly stable between 125 hours and1,500 hours when the non-fluorescent pigments are responsible for thecolor. The Standard Product C (Example 5) also demonstrated a greaterover all color change than the embodiment of Example 2. A moresignificant fact is that the Standard Product C color loss directionindicates a more significant decrease in chroma (shift to the left).This loss of color saturation in the Standard Product C (Example 5)indicates that the embodiment of Example 2 can have better visibility inreal world daytime applications.

EQUIVALENTS

[0044] While this invention has been particularly shown and describedwith references to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims. Those skilled in the artwill recognize or be able to ascertain using no more than routineexperimentation, many equivalents to the specific embodiments of theinvention described specifically herein. Such equivalents are intendedto be encompassed in the scope of the claims.

What is claimed is:
 1. An extended life fluorescent polyvinyl chloridesheeting, comprising: a) a polyvinyl chloride film having a fluorescentcolorant and hindered amine light stabilizer incorporated therein; andb) a protective polymer layer, which is attached to said polyvinylchloride film, wherein said protective layer includes an ultravioletabsorber.
 2. The sheeting of claim 1 wherein said protective layerincludes a light filtering agent, which is incorporated into saidprotective layer, said filtering agent blocks the 425 nm and lowerwavelengths of the visible spectrum.
 3. The sheeting of claim 1 whereinsaid hindered amine includes bis-(1,2,2,6,6-tetramethyl-4-piperidinyl)sebacate.
 4. The sheeting of claim 2 wherein said light filtering agentincludes Color Index Solvent Yellow
 93. 5. The sheeting of claim 1wherein said protective polymer layer includes a polymer selected fromthe group consisting of polyacrylate, polyurethane, polyurethaneacrylate, polyvinyl chloride, polyvinyl acetate and polyvinylidenechloride.
 6. The sheeting of claim 1 wherein said ultraviolet absorberis selected from the group consisting of benzophenone and benzotriazole.7. The sheeting of claim 1 wherein said protective polymer layer has athickness in the range of between about 0.2 mils and about 15 mils. 8.The sheeting of claim 1 wherein said protective polymer layer has athickness in the range of between about 0.5 mils and about 1.0 mil. 9.The sheeting of claim 1 wherein said polyvinyl chloride film includes aprinted pattern.
 10. The sheeting of claim 9 wherein said polyvinylchloride film includes a printed pattern formed of a white ink toenhance daytime chroma.
 11. The sheeting of claim 1 wherein thepolyvinyl chloride film includes a metalized layer thereon.
 12. Thesheeting of claim 11 wherein the metalized layer is formed of a metalselected from the group consisting of aluminum, chromium, gold,palladium, platinum and silver.
 13. A retroreflective structure formedwith the fluorescent polyvinyl chloride sheeting of claim 1 .
 14. Amethod for forming an extended life fluorescent polyvinyl chloridesheeting, comprising the steps of: a) providing a polyvinyl chloridefilm having a fluorescent colorant incorporated therein; and b)attaching a protective polymer layer to said polyvinyl chloride film,wherein said protective polymer layer includes an ultraviolet absorber.15. The method of claim 14 wherein said protective polymer layerincludes a light filtering agent that blocks the 425 nm and lowerwavelengths of the visible spectrum, thereby forming the extended lifefluorescent polyvinyl chloride sheeting.
 16. An extended lifefluorescent sheeting, comprising: a) a polyvinyl chloride film having afluorescent colorant and hindered amine light stabilizer incorporatedtherein; b) a protective polymer layer, which is attached to saidpolyvinyl chloride film, wherein said protective layer includes anultraviolet absorber and wherein said protective polymer layer includesa polymer selected from the group consisting of polyacrylate,polyurethane, polyurethane acrylate, polyvinyl acetate andpolyvinylidene chloride.
 17. The extended life fluorescent sheeting ofclaim 16 wherein said protective layer includes a light filtering agent,which is incorporated into said protective layer, said filtering agentblocks the 425 nm and lower wavelengths of the visible spectrum.
 18. Thesheeting of claim 16 wherein said ultraviolet absorber is selected fromthe group consisting of benzophenone and benzotriazole.
 19. The sheetingof claim 16 wherein said hindered amine includesbis-(1,2,2,6,6-tetramethyl-4-piperidinyl) sebacate.
 20. The sheeting ofclaim 16 wherein said light filtering agent includes Color Index SolventYellow 93.